Twinblade Paladin is a uncommon Creature — Human Knight card from The List (PLST), collector number M20-285. Current market price: $0.38, TCGplayer market prices via Scryfall.
Whenever you gain life, put a +1/+1 counter on this creature. As long as you have 25 or more life, this creature has double strike. (It deals both first-strike and regular combat damage.)